Printing presses are well-known devices for mass production of printed media. In certain types of printing presses, such as flexographic printing presses, a web of paper or other material is imprinted by passing the web through the press and between a rotating impression cylinder and a rotating plate cylinder. Ink is transferred from the plate cylinder onto the web in a predetermined manner corresponding to the type or other indicia on the printing plate affixed to the plate cylinder. The printed web is then processed further, such as through additional imprinting or appropriate collating, folding, cutting or other desired process, to result in the final product.
A significant problem facing manufacturers and operators of flexographic and other types of printing presses involves proper application of ink to the web. In flexographic printing, for example, the ink is applied to the plate cylinder in a precise manner by a rotating anilox metering roll. The anilox roll is positioned to abut the plate cylinder so that an edge surface of the anilox roll is in contact with an edge surface of the plate cylinder. The circumferential surface of the anilox roll typically is engraved to include a large number of recesses for holding ink in a precise volumetric manner. Ink is transferred from the anilox roll to the printing plate mounted on the plate cylinder as the anilox roll edge surface rotates against the edge surface of the printing plate.
Ink is applied to the surface of the anilox roll by an ink applicator head. The applicator head may include doctor blades which contact the anilox roll above and below the head. The applicator head, doctor blades and anilox roll surface form a closed chamber. One or more ink jets within the applicator head chamber direct a stream of ink onto the anilox roll surface as the anilox roll is rotated about the applicator head. The doctor blades serve the important purpose of removing excess ink from the surface of the anilox roll as the roll is rotated. Excess ink removed from the surface of the anilox roll by the doctor blades is collected in a reservoir provided in the applicator head chamber.
This arrangement permits ink to be precisely metered onto the plate cylinder because only the volumetric amount of ink held in the recesses on the anilox roll surface is applied to the plate cylinder with any excess ink being removed by the scraping action of the doctor blades as the anilox roll is rotated. It is essential to maintain continuous contact between the doctor blades and the surface of the anilox roll to ensure that only the desired amount of ink is metered onto the plate cylinder. Continuous contact between the doctor blades and the anilox roll surface is also Ad important to maintain a sealing relationship between the applicator head and the anilox roll surface so as to prevent leakage of ink from the printing press.
A significant problem occurs when continuous contact between the doctor blades and the anilox roll surface is broken. Contact can be broken when the doctor blades becomes worn--a common occurrence during operation of the printing press. The doctor blades can become worn for a number of reasons including, for example, from abrasion by abrasive constituents present in waterborne inks. This concern is expected to grow as the ratio of abrasive constituents in the ink increases due to removal of volatile organic compounds from the inks in order to address environmental concerns. Other factors contributing to doctor blade wear include: the degree to which the anilox roll is engraved and polished, line speed, blade pressure, blade angle, the type of material used to form the blade and whether the blade includes a beveled surface.
The continuous contact between the doctor blades and the anilox roll surface may be broken by doctor blade wear because the applicator head holding the doctor blades is typically held in a single position directly against the anilox roll at the start of the printing process. As the doctor blade surfaces become worn, a gap is formed between the doctor blades and the anilox roll surface. The position of the applicator head must be constantly monitored and adjusted to continuously reposition the doctor blades against the anilox roll surface. Failure to constantly monitor and adjust the position of the doctor blades relative to the anilox roll will result in inadequate removal of excess ink from the anilox roll and ink leakage.
An improved printing press system which would automatically and constantly adjust the position of doctor blades relative to an anilox roll to ensure proper ink distribution to a web and which would avoid ink leakage from the press would represent an important advance in the art.